Recently, engine fuel economy has been improved by reducing engine displacement and increasing the dynamic range of engines. In particular, smaller engines have been boosted to provide the performance of larger less efficient engines while increasing fuel economy by way of lower engine pumping losses. Further, by directly injecting fuel into a boosted engine, engine performance can be further improved since direct injection of fuel helps to cool the incoming charge, thereby allowing additional air into engine cylinders. However, boosting and directly injecting fuel to cylinders can also cause engine temperature to rise at a rate that is higher than that of conventionally aspirated engines. In particular, cylinder temperatures may rise quickly and impart additional heat to the vehicle cooling system since more charge is inducted to cylinders and since downsized engines may have fewer cylinders. And, since the engine temperature may have a rate of rise that is higher than that of normally aspirated port fuel injected engines, it may be more difficult to keep engine temperatures below a desired level when a torque request is made. Thus, increased engine performance and fuel economy may be achieved, but the increased engine performance may subject the engine to the possibility of operating above a desired temperature.
The inventors herein have developed a method for providing engine performance and fuel economy while at the same time reducing the possibility of heating an engine to a temperature that is greater than a desired temperature. In particular, the inventors have developed a method for controlling an engine, comprising: when engine temperature is less than a first threshold, limiting an engine temperature rate of change to be less than a first amount; and when said engine temperature exceeds the first threshold, limiting the engine temperature rate of change to be less than a second amount, said second amount less than said first amount.
The performance of an engine having a wide dynamic operating range may be preserved while the possibility of operating the engine above a desired temperature is reduced by controlling the engine in relation to engine temperature and the rate of engine temperature change. For example, when an engine is operating at a low load and the engine cooling system has excess cooling capacity, the engine may be operated at full load for intervals without limiting engine load capacity or power output. On the other hand, when the engine is operating at higher loads for an extended period of time, the engine load capacity or power output may be lowered to a level that is less than full engine power during periods when full engine power is requested. In addition, to further improve engine temperature control, the reduction of engine power output during higher engine temperature conditions can be related to (e.g., proportional to) the rate of change in engine temperature. In this way, engine power output can be controlled so that there is less possibility of operating the engine above a desired temperature when engine torque is requested.
The present description may provide several advantages. For example, the approach may reduce the possibility of engine degradation while the engine provides a desired level of performance. Further, the approach may allow an engine manufacturer to provide adequate engine cooling without having to oversize the engine cooling system. Further still, the approach can provide full power output when the cooling system has excess cooling capacity. In addition, the approach can also limit engine power output when the engine cooling system is operating at a higher utilization amount.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.